Thanks for that Kasper — your watch looks to have separate battery areas (the two batteries for the radio? and the single battery for the watch?).

With mine there's just one battery (for the watch) and the watch unit and radio unit are separate from each other. There's nowhere obvious that the batteries can go for the radio (unless power is coming down the headphone cable) so I'm still stumped

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The first FM radio watches - STEREO or not (and I have 2 of the early and very rare Stereo radio-watch pieces from early 80's ), had the radio part OF THE WATCH powered from an EXTERNAL BATTERY PACK INCLUDED IN THE HEADPHONES CORD, headphones having a (mini)jack with 3 (three!!!) dividers, not 2 as in a regular stereo headphonesThus You cannot hear anything unless You have such Headphones, with a battery pack included and THAT special minijack connector!!! Please see the below picture from Ebay from an early Armitron FM stereo watch: PIcture from:https://i.ebayimg.com/images/g/BN4AAOSwdAxZbPnd/s-l1600.jpg

And this is a regular stereo minijack, with TWO dividers NOT THREE, for the comparison! Hope this helps,

Every watch should have its own story...consequently, a watch collector has to be a good storyteller :)

That's very interesting (and confirms my suspicions/theory). On one hand they could fit a larger radio unit in the case because they didn't have to worry about batteries, or additional battery hatches, but on the other — as you say — if you don't have the powered headphones you might be out of luck with getting it working at all.

I have a few of the 3-part 3.5mm cables (the other end goes to RCA plugs) that came from old handycams, that I wonder might be usable (send 3v down the yellow plug).